Machine of Donor Livers for Transplantation: A Proposal for Standardized Nomenclature and Reporting Guidelines

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Citation Karangwa, S. A., P. Dutkowski, P. Fontes, P. J. Friend, J. V. Guarrera, J. F. Markmann, H. Mergental, et al. 2016. “Machine Perfusion of Donor Livers for Transplantation: A Proposal for Standardized Nomenclature and Reporting Guidelines.” American Journal of Transplantation 16 (10): 2932-2942. doi:10.1111/ajt.13843. http:// dx.doi.org/10.1111/ajt.13843.

Published Version doi:10.1111/ajt.13843

Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:29738961

Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA American Journal of Transplantation 2016; 16: 2932–2942 © 2016 The Authors. American Journal of Transplantation published by Wiley Periodicals Inc. Wiley Periodicals, Inc. on behalf of American Society of Transplant Surgeons doi: 10.1111/ajt.13843

Machine Perfusion of Donor Livers for Transplantation: A Proposal for Standardized Nomenclature and Reporting Guidelines

S. A. Karangwa1,2, P. Dutkowski3, P. Fontes4,5, With increasing demand for donor organs for trans- P. J. Friend6, J. V. Guarrera7, J. F. Markmann8, plantation, machine perfusion (MP) promises to be a beneficial alternative preservation method for donor H. Mergental9, T. Minor10, C. Quintini11, 12 13 14 livers, particularly those considered to be of subopti- M. Selzner , K. Uygun , C. J. Watson mal quality, also known as extended criteria donor and R. J. Porte1,* livers. Over the last decade, numerous studies researching MP of donor livers have been published 1Section of Hepatobiliary Surgery and Liver and incredible advances have been made in both Transplantation, Department of Surgery, University of experimental and clinical research in this area. With Groningen, University Medical Center Groningen, numerous research groups working on MP, various Groningen, the Netherlands techniques are being explored, often applying differ- 2Surgical Research Laboratory, University of Groningen, ent nomenclature. The objective of this review is to University Medical Center Groningen, Groningen, the catalog the differences observed in the nomenclature Netherlands used in the current literature to denote various MP 3Department of Surgery & Transplantation, University techniques and the manner in which methodology is Hospital Zurich, Zurich, Switzerland reported. From this analysis, we propose a standard- 4Thomas E. Starzl Transplantation Institute Department ization of nomenclature on liver MP to maximize of Surgery, University of Pittsburgh Medical Center, consistency and to enable reliable comparison and Pittsburgh, PA meta-analyses of studies. In addition, we propose a 5McGowan Institute of Regenerative Medicine, standardized set of guidelines for reporting the University of Pittsburgh, Pittsburgh, PA methodology of future studies on liver MP that will 6Nuffield Department of Surgery, Oxford Transplant Centre, facilitate comparison as well as clinical implementa- University of Oxford, Churchill Hospital, Oxford, UK tion of liver MP procedures. 7Department of Surgery, Center for Liver Disease and Transplantation, Columbia University Medical Center, Abbreviations: MP, machine perfusion; PRISMA, New York, NY Preferred Reporting Items for Systematic Reviews 8Transplant Center, Massachusetts General Hospital, and Meta-Analyses; SCS, static cold storage Boston, MA 9Liver Unit, University Hospital Birmingham, Birmingham, UK Received 15 February 2016, revised 28 March 2016 10Department of Surgical Research, Clinic for General and accepted for publication 19 April 2016 Visceral and Transplantation Surgery, University Hospital Essen, Essen, Germany 11Department of Surgery, Transplant Center, Digestive Disease Institute, Cleveland Clinic Foundation, Cleveland, OH, 12Department of Surgery, Multi Transplant Introduction Program, Toronto General Hospital, Toronto, ON, Canada 13Department of Surgery, Center for Engineering in In an effort to meet the demand for donor organs needed Medicine, Massachusetts General Hospital, Harvard for transplantation, livers considered to be of suboptimal Medical School, Boston, MA quality and function are increasingly being transplanted. 14University of Cambridge Department of Surgery and Given the increased vulnerability of these organs and the the NIHR Blood and Transplant Research Unit in Organ potential injury incurred during procurement and storage/ Donation and Transplantation University of Cambridge, transportation, machine perfusion (MP) is a promising Addenbrooke’s Hospital, Cambridge, UK alternative to static cold storage (SCS), the current stan- *Corresponding author: Robert J. Porte, [email protected] dard of care in donor liver preservation. Following the first successful series of extra-corporeally perfused canine liver This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs grafts performed by Brettschneider and Starzl et al. in License, which permits use and distribution in any 1967 (1), MP has been explored as a method to achieve medium, provided the original work is properly cited, the the preservation of donor livers under conditions simulat- use is non-commercial and no modifications or ing normal in vivo physiology in an attempt to minimize adaptations are made. -related injury associated with SCS. Research into

2932 Standardization of Nomenclature and Reporting of Liver Machine Perfusion

MP has established three major benefits: the capability to was conducted using the medical subject heading (MeSH) terms and preserve donor organs while providing them with oxygen Emtree keywords “machine perfusion, machine preservation, liver and nutrients at various temperatures (optimal and pro- transplantation, and hepatic transplantation” combined with free text longed preservation); the ability to recondition and opti- terms regarding machine perfusion of donor livers such as “hypothermic,” “normothermic,” and “subnormothermic.” mize the function of donor organs, particularly extended criteria organs, with, for instance, oxygen perfsufflation, Selection criteria and data collection de-fatting techniques for steatotic livers and pharmaceuti- Study selection was performed independently by two authors (S.A.K and cal intervention (organ resuscitation and function recov- R.J.P.) in a standardized fashion using the Preferred Reporting Items for ery); and lastly, to provide the possibility of testing the Systematic Reviews and Meta-Analyses (PRISMA) method (2). Study function and viability of the organ prior to transplantation inclusion was carried out in three phases. An initial title search was car- (ex situ viability testing) by MP at 37°C. ried out whereby relevant titles were screened and studies whose titles were unrelated to the aims of this review were excluded. The abstracts With the number of publications on liver MP to date of the remaining studies were then acquired and independently assessed exceeding 500, the last 10 years has seen an incredible for eligibility. Full papers of the abstracts regarded as potentially eligible advancement in both experimental and clinical research were retrieved and underwent complete review and assessment until a final compilation of articles was made. For articles in which an inconsis- into donor liver MP. Several groups have been exploring tency between the two authors occurred, a discussion about these arti- different methods of MP with the major technique differ- cles was held to reach to a consensus. Figure 1 illustrates the study ences relating to the temperatures used and the provision selection procedure and the inclusion and exclusion criteria. of oxygen and whether the technique is flow or pressure controlled. Given that MP is a nascent technology with Inclusion criteria: many technical aspects continuing to be explored, adapted and improved, the publications on MP have exhibited great • All articles on machine perfusion of donor livers discrepancies. These include the nomenclature used to • Fully accessible articles written in English and published in scientific describe the different MP techniques (abbreviations journals • included), the temperatures considered to be hypo-, sub- Human and animal studies normo, or normothermic and the manner in which certain details of the methodology are reported. The absence of standardized nomenclature and guidelines for reporting Article titles identified in technical details pertaining to MP gives rise to the rela- all databases n= 2265 tively large variation that exists among studies. This makes it difficult to compare different studies, perform meta-ana- Irrelevant titles lyses and, in some cases, attempt to reexecute the excluded n= 1406 methodology used.

With the number of clinical studies on MP of donor liv- Abstracts ers rapidly increasing, it is important that a consensus n= 859 is reached on the nomenclature applied and which nec- essary aspects of the methodology should be included Duplicates excluded n= 287 in a paper. The objective of this review is to catalog the Irrelevant abstracts excluded n= differences observed in the nomenclature used in the 291 current literature to denote various techniques of liver Unfound full articles n=27 MP and the manner in which the methodology is Full papers described. From our analysis, we aim to address these n= 254 Irrelevant articles n= 86 discrepancies, propose recommendations for nomencla- ture and develop a standardized set of guidelines for Reviews n= 25 the reporting methodology for future studies on MP of Non-English n= 16 donor livers.

Included articles n=127 Methods

Literature search strategy Figure 1: Flow chart illustrating study selection and inclu- A comprehensive literature search for all published articles regarding MP sion procedure. Irrelevant titles included studies mainly involv- of donor livers was performed using the PubMed, EMBASE, MEDLINE, ing in vivo perfusion (and not machine perfusion), in vitro cell Web of Science, and Cochrane Library databases. The final date of the studies, follow-up studies on MP or studies involving analysis of search was February 17, 2015. To ensure all potentially relevant articles data from studies on MP of donor livers without including the were included in the search, no specific date limits were set. The search MP procedure description in the methodology.

American Journal of Transplantation 2016; 16: 2932–2942 2933 Karangwa et al

Exclusion criteria: performed MP for various time periods after a few hours of SCS (during transport of the organs from the donor to • Irrelevant to title and objective of review recipient centers) or as a result of prolonged cold ische- • Non-English mia times due to various logistical or unforeseen circum- • Articles about MP of other organs stances (36–50). Interesting to note, as opposed to • Full version inaccessible performing MP for the entire preservation phase, the first clinical studies conducted by Guarrera et al. and Data extraction and analysis The data from the included studies was assessed, with the main focus Dutkowski et al. chose to focus on exclusively conduct- of these articles being the Materials and Methods section. The primary ing MP after a period of traditional SCS and immediately aim of this study was to investigate the manner in which the methodol- prior to implantation (<2 h prior) (35,40,45,46,51). ogy of these studies was reported and to determine how certain aspects concerning the MP procedure were mentioned. The recommendations and guidelines that this review provides were extensively discussed and Nomenclature and abbreviations used to identify the agreed on by all authors of this paper. type of machine perfusion As the pioneering technique of MP, a number of differ- ent terms, as shown in Table 1, have been used to Results describe hypothermic MP in the past two decades. Even though the majority of the studies mention the term hy- Of the 2265 articles identified from the initial literature pothermic within the title and/or article itself, a number search, 127 of these ultimately met all inclusion criteria of papers simply use the term machine perfusion, with- (Figure 1). These papers were published between 1997 out specific indication of the temperature used. Other and 2015 and constituted both animal and human clinical types of MP include subnormothermic and normothermic studies. From our analyses, we observed several differ- perfusion. For all three major types of MP, despite refer- ences in the manner in which the same type of MP tech- ring to the same procedure, numerous abbreviations are niques was referred to as well as marked variation in the used to describe the type of MP performed (Table 1). temperatures used. In the following paragraphs and tables, we highlight and assess these differences as well Additionally, for subnormothermic and normothermic as provide recommendations to establish uniformity in MP, a major difference lay in the additional emphasis of the manner in which data are reported. whether these perfusions were performed extra corpore- ally or not. Timing of machine perfusion In all of the studies reviewed in this paper, MP was con- Temperatures used during machine perfusion ducted either for (almost) the entire duration of the Although, in general, three types of MP can be recog- preservation phase of the transplantation process or nized (i.e. hypothermic, subnormothermic and normother- before or after a period of traditional SCS. A significant mic), we noted marked inconsistency in the actual majority of the research groups that conducted animal temperatures denoted by these terms (see Table 2). studies (3–34) and studies in which the donor and recipi- Despite including a description of the technique of MP, a ent center was the same location (35) nearly eliminated number of papers (7,15,52,53) failed to specify what par- the SCS phase, thus perfusing donor organs immediately ticular temperatures were used in their respective stud- after procurement until the point of implantation. The ies while some descriptions used arbitrary and unspecific remaining studies, particularly most human studies,

Table 1: Nomenclature and abbreviations currently used for the different types of liver machine perfusion Type of machine perfusion References Hypothermic (oxygenated) machine perfusion (HMP) 1–8,15,22,24,26,30,31,35,41–46,48–50,56,71,72,80,82,88–99 Hypothermic oxygenated perfusion (HOPE) 8,9,13,34,51,61,100–107 Continuous hypothermic oxygenated machine perfusion (CHOP) 108 Machine perfusion (MP) or Machine perfusion preservation (MPP) 53,57,63,64,73–75,109–111 Cold perfusion 23 Subnormothermic machine perfusion (SMP) 11,112 Subnormothermic machine perfusion (SNMP) 3,10,18,39,76,113–115 Subnormothermic ex vivo liver perfusion (SNEVLP) 17 Subnormothermic machine perfusion (MP20) 60,65–67,116–118 Normothermic machine perfusion (NMP) 16,19,21,25,29,36–38,40,62,68,81,119–123 Normothermic extracorporeal perfusion (NELP) 12,14,77,124,125 Normothermic extracorporeal perfusion (NECMO) 83 Normothermic ex vivo liver perfusion (NEVLP) 5 Warm perfusion 33,54,55,62

2934 American Journal of Transplantation 2016; 16: 2932–2942 Standardization of Nomenclature and Reporting of Liver Machine Perfusion

Table 2: Various temperatures currently used for the different studies that provided oxygenation during MP explicitly sta- types of liver machine perfusion ted this in the methodology; however, a number of studies References went further to specifically outline the details such as the O2/CO2 mixture or the oxygen tension (2,3,5,6,44,64–78) Hypothermic temperatures as opposed to simply mentioning the presence of an ° – ° 0 C 4 C 126 oxygenator within the MP system (6,11,18,20,22,24,59, ° – ° 1 C 3 C 127 60,62,64–68,79–81). Lastly, a significant number of the 2°C 1°C 119 studies also clearly mentioned the type of pump used dur- 3°C–5°C50 – – – 3°C–6°C 47,48 ing MP (2,3,5,6,26,64 67,69 78,82 84), which gives an 4°C 4,8,50,53,74,75,78,100,110,111 indication of the flow pattern through the liver. 4°C–6°C 27,29,30,41,63 4°C–8°C 12,21,63 5°C 121 Discussion 5°C–8°C 122–125 8°C 60,61 In an effort to initiate and facilitate a standardization of ° – ° 8 C 10 C77 nomenclature as well as to establish guidelines on the ° – 10 C 24,49,53 57,83,126 experimental and clinical reporting of MP of donor livers, Subnormothermic temperatures this systematic literature review assessed the differ- 20°C 68,80,81,93,95,96,121,127 21°C 11,69,70,78,82,88,89,128 ences in the nomenclature, temperatures and techniques 25°C71 currently used and reported in published articles. 33°C90 20°C–30°C94 The timing of machine perfusion Normothermic temperatures Given that the timing and duration of MP during the Porcine 38°C 100,101,106,116 entire preservation and transportation period is essen- Human 35.5°C–37.5°C76 tially correlated to the specific benefits MP is intended to ° – ° Rat 36.5 C 37 C 129 provide to the organ, it is important that the period at ° – Human/rabbit/rat 37 C 9,52,74,75,102 105,110,114,130 which MP is performed is specified, for instance, organ Rat 37.5°C 14,121,125 reconditioning and optimization can be applied either (Porcine) 39°C97 “Warm” 33,52 prior to or after static cold storage, whereas viability test- ing is generally performed shortly before implantation. terms such as “warm,” “cold,” or “room temperature” It is evident from the reviewed literature that MP can be (23,33,39,54,55) to denote the temperatures used during performed mainly at three particular time points; (1) MP. Of the 58 studies on hypothermic MP, 26 (45%) immediately after , before the organ reported perfusing the livers at 4°C, whereas the rest is stored on ice for transportation (prestatic cold storage); performed MP at different temperatures within the 0°C– (2) (shortly) before organ implantation, especially in 10°C range. All studies on subnormothermic MP were instances with longer cold ischemia times (poststatic cold generally conducted at temperatures between 20°C and storage); and (3) for the entire preservation period 30°C. However, the majority of these studies reported between procurement and implantation, thus (nearly) using 20°Cor21°C, which in all cases the authors eliminating the need for SCS. In the case of the latter referred to as being room temperature. Normothermic method, we propose the term preservation MP. When MP was primarily carried out at the physiological body applying preservation MP, a short period of SCS is still temperature of humans or the animal of study, although required during and immediately after organ procurement, small discrepancies were seen in the temperatures sta- when the organ is prepared for connection to the perfu- ted as being the physiological body temperature of the sion device, and shortly before implantation to avoid different animals. warm ischemia during the anastomosis time. We thus propose to use the term preservation MP when the time Other aspects of methodology period of SCS either before or after MP is less than a In addition to the discrepancies in temperature, analysis of maximum of 3 h (Figure 2). This 3-h time frame is based the literature exhibited variation in the description of cer- on the experience of the authors of this paper with vari- tain technical aspects of the machine perfusion procedure. ous techniques of machine perfusion. It was generally For instance, seven studies lack a clear description of agreed that in reality it normally takes approximately 1.5– whether the liver underwent single (via the hepatic artery 2 h from the point of in situ cold flush, donor hepatec- or portal vein) or dual perfusion (16,23,24,56–59). As tomy, back table procedure to connection of the organ opposed to the vast majority (92%) of the studies that stip- onto the perfusion device. However, there are a number ulated the use of a pressure or flow controlled system and of cases in which this may be delayed, for example, in liv- provided specifications of the settings used, a number of ers with aberrant arterial vasculature that require vascular studies failed to specify this (7,12,16,24,56,59–65). All reconstructions, and thus extra back table time is needed

American Journal of Transplantation 2016; 16: 2932–2942 2935 Karangwa et al

SCS ≤ 3 hr SCS ≤ 3 hr

SCS Post-SCS MP

Pre-SCS MP SCS Procurement Transplantation Preservation MP

Donor hospital Transportation Transplant center

Time

Figure 2: Charts illustrating classification of the timing of machine perfusion. MP conducted within 3 h of organ procurement and followed by a period of SCS is considered as pre-SCS MP, whereas that performed after a period of at least 3 h of SCS preservation prior to implantation is considered as post-SCS MP. Additionally, MP can be performed between periods of SCS. Duration of SCS and preserva- tion MP conducted within the 3 h windows on either end of the procedure remains unspecified and can be widely varied. Lastly, MP can also be performed for the entire preservation period (immediately after organ procurement until just before implantation).

100

90

80

70

60

50

40

30

Percentage of [%] Percentage 20

10 NMP SNMP MMP HMP 0 40 35 30 25 20 15 10 5 0 Temperature [˚C]

Figure 3: Graphic presentation of the change in the rate of metabolism with decreasing temperature. Based on Van’t Hoff’s 10=ðt2t1 Þ principle (expressed as Q10 ¼ ðÞk2=k1 ), this graph demonstrates the significantly reduced metabolism at hypothermic tempera- tures (0°C–12°C). The vertical lines in the graphs indicate the lower endpoint of temperature ranges of the different types of MP proposed. NMP; normothermic machine perfusion (35°C–38°C); SMP, subnormothermic machine perfusion (25°C–34°C); MMP, mid-thermic machine perfusion (13°C–24°C); HMP, hypothermic machine perfusion (0°C–12°C). before the liver can be connected to the device. This 3-h machine perfusion fluid, remove the cannulas and per- time frame is therefore the recommended maximum time form the last back table work (i.e. trimming of vessels period that allows for unavoidable circumstances that and preparation of the venacava in the donor for piggy may cause a delay before machine perfusion can be back anastomosis), one may expect a total time period started. Similarly, it generally takes 40–60 min to make of 1–3 h before reperfusion in the recipient the vascular anastomoses in the recipient until reperfu- occurs. Therefore, this 3 h of SCS reflects a maximum sion can be initiated. When this is added to the time time period. If the duration of SCS is longer than 3 h needed to take a donor liver off the machine, flush out and MP is applied either prior (immediately after

2936 American Journal of Transplantation 2016; 16: 2932–2942 Standardization of Nomenclature and Reporting of Liver Machine Perfusion procurement) or after SCS (shortly before implantation), temperatures as low as 15°C, 18°Cor20°C are too low we propose to call this pre-SCS MP and post-SCS MP, to be considered as subnormothermic as not only does respectively. this term suggest being slightly below normal body temperature but also at such low temperatures a living Nomenclature and abbreviations person would be defined as (extremely) hypothermic. A number of different terms and abbreviations have been Whereas at higher temperatures such as 30°C–33°C, the used in the observed studies describing generally similar rate of metabolism increases close to 70% of the normal MP methods. In some of these cases, a few aspects rate at body temperature (Figure 3). Based on this, ° – ° such as oxygenation or single/dual perfusion may have we propose to use the term mid-thermic (13 C 24 C) differed and were incorporated. To minimize confusion to distinguish the lower temperatures (0°C–12°C) from and tackle the heterogeneity in the nomenclature, we the less physiologically abnormal subnormothermic ° – ° believe that authors of future publications should avoid temperature range (25 C 34 C). adapting other aspects of perfusion into the nomencla- ture and retain simplicity. Given the importance of speci- fying certain aspects of MP performed, the choice to use certain terms in the title and throughout the publication Table 3: Checklist with recommended guidelines for the remains within the discretion of the author, although it is reporting of relevant aspects of the methodology used in liver advised that the use of the standardized abbreviations machine perfusion for the respective types of MP—HMP (hypothermic 1. Phase of Timing machine perfusion), MMP (mid-thermic machine perfu- preservation ○ Pre-SCS MP sion), SMP (subnormothermic machine perfusion) and ○ Preservation MP NMP (normothermic machine perfusion)—be maintained. ○ Post-SCS MP Duration of MP ○ Specified in hours/minutes Temperature ranges 2. Environment In situ As described in the Results section, experiments con- and temperature ○ (Normothermic) Regional perfusion ducted on MP of donor livers have generally been per- Ex situ: formed at three temperature ranges: hypothermically at ○ Hypothermic MP (0°C–12°C) 0°C–10°C,subnormothermically at 20°C–33°C and nor- ○ Midthermic MP (13°C–24°C) mothermically at 35°C–38°C (depending on the species ○ Subnormothermic MP (25°C–34°C) used in study). Based on common practice of the various ○ Normothermic MP (35°C–38°C) research groups working on liver MP and following a dis- 3. Technical Single or dual vessel perfusion cussion with the authors involved in this review, the fol- aspects (hepatic artery/portal vein) ○ lowing classification of the standardized temperature Continuous or pulsatile flow Pressure or flow controlled perfusion ranges is proposed. ○ Computerized or manually controlled system Hypothermic MP (0°C–12°C): All studies involving HMP Perfusion temperature so far have been conducted at temperatures of 10°C ○ Specify temperature in °C and below with the major reason being that the rate of ○ Specify any significant metabolism and enzymatic reactions in mammalian cells temperature changes during MP decreases to rates as low as 20% or even less (85,86) (e.g. gradual rewarming) (Figure 3). The benefit of HMP is that it minimizes Temperature control preservation injury while improving organ viability and, ○ Automated or manual for oxygenated livers, replenishes adenosine tri- Type of pump ○ Roller/centrifugal/peristaltic phosphate (ATP) stores. Because the rates of numerous 4. Perfusion fluid Perfusion fluid components energy dependent reactions of liver mitochondrial composition and ○ Full description of the composition enzymes exhibit a significant change at 12.5°C (87), the oxygenation of the perfusion fluid used1 proposed cut-off point for HMP is 12°C. Oxygenation ○ Ambient air, pure (100%) oxygen, or carbogen, other mixture Midthermic MP (13°C–24°C) and subnormothermic Heparin, antibiotics and nutrients MP (25°C–34°C): The term subnormothermic has been Any other interventions e.g. drugs considered for temperature ranges varying between 5. Pre- and Is organ flushed before and/or after MP? 12°C and 35°C even though MP was performed at Post-MP phase ○ Which fluid is used and how much? 20°C–22°C in the majority of studies in which the ○ At what temperature? temperature was referred to as subnormothermic. This Specify vessels used in flushing of broad temperature range shows a great difference in the the organ rate of metabolism at, for example, 12°C as compared to 1Both at baseline as well as compounds that are continuously or 33°C (Figure 2). Furthermore, it can be argued that intermittently administered during perfusion.

American Journal of Transplantation 2016; 16: 2932–2942 2937 Karangwa et al

Normothermic MP (35°C–38°C): The term normo- reporting of technical aspects of MP is required to mini- thermic should refer to the normal core body temperature mize heterogeneity and to facilitate more reliable and of the species used in the study, i.e. 37°C for human and valid comparison analyses of studies. We hope this rodent studies and 38°C in studies with porcine models. paper provides a useful overview on current nomencla- ture and will be helpful in the reporting of future research studies on liver MP. Ex vivo or ex situ MP An additional aspect of MP that demonstrated particular variation in the literature was the referral of MP as being Disclosure performed ex vivo or ex situ. Given that MP involves per- fusion of donor livers outside the body of a deceased The authors of this manuscript have no conflicts of inter- donor, the term ex vivo, which refers to “outside of the est to disclose as described by the American Journal of living body,” does not seem appropriate. Therefore, the Transplantation. term ex situ, which refers to “outside original location/ position,” is proposed as a more representative descrip- tion of what occurs during MP. References

Other technical aspects and reporting guidelines 1. Yanaga K, Makowka L, Lebeau G, et al. A new liver perfusion Along with discrepancies in the nomenclature and tem- and preservation system for transplantation research in large – perature ranges, reporting of other aspects, particularly animals. J Invest Surg 1990; 3: 65 75. 2. Moher D, Shamseer L, Clarke M, et al. Preferred reporting technical aspects belonging to methodology, were items for systematic review and meta-analysis protocols observed. Given the ongoing advancement in the field (PRISMA-P) 2015 statement. Syst Rev 2015; 4: 1. of MP, it is important that certain methodological 3. Berendsen TA, Bruinsma BG, Lee J, et al. A simplified subnor- aspects are explicitly stated to ensure that studies can mothermic machine perfusion system restores ischemically be reproduced as well as objectively compared with damaged liver grafts in a rat model of orthotopic liver transplan- each other. Moreover, with additional clinical trials cur- tation. Transplant Res 2012; 1: 6. rently being performed, this will facilitate future meta- 4. Berendsen TA, Bruinsma BG, Puts CF, et al. Supercooling analyses with maximum validity and reliability. The enables long-term transplantation survival following 4 days of authors of this review reached a consensus on various liver preservation. Nat Med 2014; 20: 790–793. aspects of the MP procedure that were considered fun- 5. Boehnert MU, Yeung JC, Bazerbachi F, et al. Normothermic acellular ex vivo liver perfusion reduces liver and bile duct injury damental and developed a checklist that can be utilized of pig livers retrieved after cardiac death. Am J Transplant and referred to when preparing a report on liver MP 2013; 13: 1441–1449. (Table 3). Important aspects in this checklist include 6. Carnevale ME, Balaban CL, Guibert EE, Bottai H, Rodriguez JV. clear descriptions of the flushing technique, all of the Hypothermic machine perfusion versus cold storage in the res- technical aspects of the MP procedure, type of perfu- cuing of livers from non-heart-beating donor rats. Artif Organs sion fluid used and clarification of the time point, dura- 2013; 37: 985–991. tion and temperatures at which MP is conducted. 7. Compagnon P, Clement B, Campion JP, Boudjema K. Effects of Furthermore, to make valid comparisons of experimental hypothermic machine perfusion on rat liver function depending outcomes, the manner in which data is presented and on the route of perfusion. Transplantation 2001; 72: 606–614. described, particularly in the Results section of publica- 8. Dutkowski P, Furrer K, Tian Y, Graf R, Clavien P. Novel short- term hypothermic oxygenated perfusion (HOPE) system pre- tions, is important. The selection of (clinically) relevant vents injury in rat liver graft from non-heart beating donor. Ann endpoints during MP was not the objective of this Surg 2006; 244: 968–976; discussion 976-7. paper, but the reader is referred to other recent reviews 9. Dutkowski P, Schonfeld S, Odermatt B, Heinrich T, Junginger that have summarized the various types of biomarkers T. Rat liver preservation by hypothermic oscillating liver perfu- that can be used during MP for graft viability assess- sion compared to simple cold storage. Cryobiology 1998; 36: ment (69,70). Naturally, in clinical trials traditional out- 61–70. come parameters such as graft and patient survival 10. Fujiyoshi M, Taketomi A. Sub-normothermic machine perfusion rates, as well as hepatic and systemic postoperative preservation for graft selection and therapy in a mouse liver complications, will be relevant endpoints. In case of transplantation model. Hepatology 2014; 60: 241A–241A. donation after cardiac death (DCD) , 11. Gringeri E, Bonsignore P, Bassi D, et al. Subnormothermic machine perfusion for non-heart-beating donor liver grafts a major clinical endpoint should be the incidence of preservation in a swine model: A new strategy to increase the postoperative biliary complications. donor pool? Transplant Proc 2012; 44: 2026–2028. 12. Habib MM, Hafez TS, Parkes HG, Seifalian AM, Fuller BJ, Davidson BR. A comparison of bile composition from heart- Conclusion beating and non-heart-beating rabbit organ donors during normothermic extracorporeal liver perfusion: Experimental As experimental and clinical research into MP of donor evaluation using proton magnetic resonance spectroscopy. livers advances, a standardization of nomenclature and Transplant Proc 2004; 36: 2914–2916.

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